1. Field of the Invention
The present invention relates to an apparatus and method for adjusting the filter tap length of an adaptive equalizer, and more particularly, to an apparatus and method for adjusting the filter tap length of an adaptive equalizer using a training sequence, and for determining a required filter tap length by using multipath information detected from correlation values of synchronization symbols of a segment for data synchronization, training sequence symbols for field synchronization and input data, and from auto correlation values of the training sequence symbols. The present application is based on Korean Patent Application No. 00-33921 filed Jun. 20, 2000.
2. Description of the Related Art
A vestigial side band (VSB) digital transmission system has a transmitter for receiving data, converting the data input into a transmission format, and transmitting the converted data through a transmission channel, and a receiver for converting the data received from the transmitter through a transmission channel into a reception format and transmitting the converted data.
FIG. 1A shows a data frame of a VSB transmission system. A frame consists of segments which have 832 symbols each, and each of the segments includes four symbols of segment synchronization (to be abbreviated as ‘sync’ hereinafter) signal, 828 symbols of data and a FEC (Forward Error Correction) signal. Each data frame has 313 segments, one of which is a data field sync segment containing training sequence and 312 of which are general data segments. FIG. 1B shows a data field sync segment. The training sequence is a signal contained in the field sync signal, transmitted from the transmitter to the receiver, used as a field sync signal with pseudo noise (PN) symbols of 511/63/63/63 and 511/63/-63/63 alternating. In other words, while the training sequences in odd fields are identical with the training sequences in even fields, the signs of the second ones among three consecutive PN 63 sequences are opposite to each other.
An adaptive equalizer is a system element used in the receiver for compensation of channel distortion, such as tilt and ghost, caused by defective system elements that are in a transmission channel or a receiver. The number of taps of the adaptive equalizer is generally determined by the maximum range of ghosts to be canceled. In order to detect and cancel ghosts, 63 symbol sequences, that is, PN 63 sequences, in which symbols of training sequences are alternately reversed, have been conventionally used, which is similar to a ghost canceling method using a group coded recording (GCR) in conventional analog television systems.
The conventional ghost canceling method using the PN 63 sequences, however, has the following problems.
First, since only 63 symbols are used, the range of detecting and canceling ghosts is limited. For example, in the case of a VSB signal having a symbol rate of 10.75 MHz, post-ghosts of approximately +5.86 μs can only be canceled, which is a very limited range when compared with the existing VSB adaptive equalizer standard in which ghosts of 18.76 μs can be canceled.
Second, in order to cancel ghosts in a similar way to that adopted by the existing NTSC (National Television System Committee) analog transmission system, at least two PN 63 sequences must be examined, which may cause a delay in ghost detection time. In other words, since the conventional ghost detecting and canceling method utilizes the properties of PN 63 sequences, the signs of which, either positive (+) or negative (−), alternate at field sync signals, ghost information cannot be known until at least two field sync signals constituting one frame are processed.